Many industrial processes require the formation of layers of a material on a substrate or base. These processes include Ink Jet Printing, Photolithography and DuPont's Fodel® technology.
Ink Jet Printing
Ink jet printing is one well-known process that can be used to apply a layer of one material on a substrate. In most cases, ink jet printing is employed to place tiny droplets of ink onto a sheet of paper to create text or an image.
One kind of ink jet printer employs “thermal bubble” or “bubble jet” technology, in which ink is heated in a print head that includes hundreds or nozzles or orifices. The high levels of heat generated by resistors built into the print head vaporize the ink, and forms a series of single bubbles of ink which are propelled out of the nozzles toward a sheet of paper. In another kind of ink jet printing, an array of piezo-electric crystals is activated to vibrate and expel ink from a corresponding array of nozzles.
Both types of ink jet printers are remarkably accurate. A typical ink jet print head has 300 to 600 nozzles, and can form dots of many different colors of ink that are as small as 50 microns in diameter. All of the nozzles can be activated at once to produce complex applications of ink on paper that can even approach or match the resolution of conventional silver halide photography.
Although ink jet printing offers a relatively versatile and inexpensive process for applying a material to a substrate, ink jet printing is generally limited to placing exceedingly thin layers of ink on paper or cloth which are essentially two-dimensional. The viscosity ranges for ink jet printing are limited to ranges of one to ten cp. This limited range of viscosity in turn limits the variety of materials which may be deposited.
Photolithography
Photolithography is a purely planar process that is typically used in the semiconductor industry to build sub-micron structures. Photolithography may be used to build features in the 1˜100-micron range, but is plagued by many severe limitations:                1) The thickness of the features ranges from 0.01 to 1 microns. As a result, mechanical connections may not be made to layer built using a photolithographic layer.        2) The photolithographic process is purely planar. Photolithographic structures formed on a substrate do not include three-dimensional features having a height of more than one micron.        3) Photo lithographical processes, which use a process of vaporization of the deposited metal, needs to be run in a vacuum chamber at a temperature which supports the high temperature required to vaporize the metal.        4) Finally, photolithography requires a mask.Fodel® Materials        
According to the DuPont Corporation, Fodel® materials incorporate photosensitive polymers in a thick film. Circuit features are formed using UV light exposure through a photomask and development in an aqueous process. Fodel® dielectrics can pattern 75 micron vias on a 150 micron pitch, and Fodel® conductors can pattern 50 micron lines on a 100 micron pitch. Fodel® materials extend the density capability of the thick film process to allow densities typically achievable using more costly thin film processes.
Fodel® is a process in which a thick film is placed on the substrate. A mask is then used to expose areas of the thick film to cure the material. The substrate is then chemically etched to remove the uncured material. The Fodel® process canbe performed in an ambient environment. The limitations to Fodel® are:                1) The Fodel® process is purely planar. No three-dimensional features can be produced.        2) The Fodel® process uses a chemical etching process which is not conducive to all substrates.        3) Like photolithography, the Fodel® requires a mask.        4) The material costs of the Fodel® process are relatively high.        5) The Fodel® process is limited to features larger than 50 microns.        
Other techniques for directing a particle to a substrate involve the use of lasers to create optical forces to manipulate a source material. “Optical tweezers” allow dielectric particles to be trapped near the focal point of a tightly focused, high-power laser beam. These optical tweezers are used to manipulate biological particles, such as viruses, bacteria, micro-organisms, blood cells, plant cells, and chromosomes.
In their article entitled Inertial, Gravitational, Centrifugal, and Thermal Collection Techniques, Marple et al. disclose techniques which may be used to collect particles for subsequent analysis or for particle classification.
TSI Incorporated describes how a virtual impactor works on their website, www.tsi.com.
Another method for applying a source material to a substrate is described in a co-pending and commonly-owned U.S. patent application Ser. No. 09/584,997 filed on Jun. 1, 2000 and entitled Particle Guidance System by Michael J. Renn. This Application discloses methods and apparatus for laser guidance of micron-sized and mesoscopic particles, and also furnishes methods and apparatus which use laser light to trap particles within the hollow region of a hollow-core optical fiber. This invention enables the transportation of particles along the fiber over long distances, and also includes processes for guiding a wide variety of material particles, including solids and aerosol particles, along an optical fiber to a desired destination.
The co-pending Application by Renn describes a laser beam which is directed to an entrance of a hollow-core optical fiber by a focusing lens. A source of particles to be guided through the fiber provides a certain number of particles near the entrance to the fiber. The particles are then drawn into the hollow core of the fiber by the focused laser beam, propagating along a grazing incidence path inside the fiber. Laser induced optical forces, generated by scattering, absorption and refraction of the laser light by a particle, trap the particle close to the center of the fiber and propels it along. Virtually any micron-size material, including solid dielectric, semiconductor and solid particles as well as liquid solvent droplets, can be trapped in laser beams, and transported along optical fibers due to the net effect of exertion of these optical forces. After traveling through the length of the fiber, the particles can be either deposited on a desired substrate or in an analytical chamber, or subjected to other processes depending on the goal of a particular application.
The problem of providing a method and apparatus for optimal control of diverse material particles ranging in size from individual or groups of atoms to microscopic particles used to fabricate articles having fully dense, complex shapes has presented a major challenge to the manufacturing industry. Creating complex objects with desirable material properties, cheaply, accurately and rapidly has been a continuing problem for designers. Producing such objects with gradient or compound materials could provide manufacturers with wide-ranging commercial opportunities. Solving these problems would constitute a major technological advance, and would satisfy a long felt need in the part fabrication industry.